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Item type:Publication, Access status: with files , Enhancement of an innovative current turbine based on magnetic restorationThis doctoral thesis investigates the stability, efficiency, and fatigue life of an innovative turbine designed to extract energy from renewable flow resources through theoretical, numerical, and experimental studies. The turbine is based on the phenomenon of torsional galloping with magnetic restoration, introduced here as a novel concept. Energy extraction is enabled by the unstable dynamic behaviour of the turbine; consequently, stabilisation of the oscillatory motion must be avoided. To exploit this instability efficiently, a magnetic restoring torque is incorporated into the system. This magnetic restoration allows the oscillation amplitude of the turbine to be controlled, thereby limiting excessive vortex shedding and reducing energy losses. A linearized and a non-linear mathematical model were developed and solved. Their predictions were compared with computational simulations and experimental measurements obtained in a current channel. The stability analysis classifies the system response into spiral sink, spiral source, source, and saddle-type solutions and demonstrates that the regions exhibiting the greatest instability coincide with those of highest efficiency. The damping associated with the power take-off system was identified as the dominant parameter, with an optimum value of 0.45. Under these conditions, a maximum efficiency of 56.8% was obtained for a blade limit angle of 30°, a/c = 0.75, and Re = 15 × 10⁴. This corresponds to 95.78% of the Betz limit of 59.3%, with an estimated fatigue life of approximately 21 years. The proposed turbine therefore represents a promising concept for energy generation in remote regions without access to conventional electricity infrastructure and may contribute to the diversification of renewable energy technologies. Finally, the applicability of the concept is investigated for a river in the Amazon Basin. The resulting plant configuration is shown to satisfy the local electricity demand using a relatively small number of turbines and at a lower cost than the alternative configurations considered. The numerical simulations were conducted at the Institute for Fluid Dynamics and Ship Theory (FDS) at Hamburg University of Technology (TUHH), while the experimental investigations were carried out at the Laboratory of Waves and Currents (LOC) at COPPE/UFRJ.Publicationtype: Doctoral Thesis79 14 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Production, scaling and application of nanostructured metal multilayers as post-weld treatment(2023); Cu/Ni Nanostructured Metal Multilayer coatings are introduced as a new post-weld treatment method. Steel specimen with a double V-groove butt-weld are coated with a Cu/Ni NMM coating with an overall thickness of 9 μm, consisting of a 1 μm Ni base layer, a nanolaminate structure with a bilayer thickness of 50 nm and Cu and Ni single layer thicknesses of 15 nm and 35 nm respectively. The coating is electroplated onto the steel substrate with a single bath method. The coated steel specimens are tested in tension-tension fatigue and the corresponding S-N curves are calculated from the fatigue results. SEM, TEM and EDX investigations provide insights into the material characterization of the nanolaminate structure and the understanding of NMM failure mechanisms.Publicationtype: Doctoral Thesis63 150 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Fracture mechanics simulation of welded joints at sub-zero temperatures considering the weld shape(2022-01-27)Welded joints are the most common method for connecting steel components, but they are also points of weakness, as they contain, among other things, initial cracks or are unwelded gaps. Most of the fatigue life of a welded joints takes place during the phase of macro crack growth, fracture mechanics models are therefore widely used method to predict the fatigue life. In this thesis, a procedure is developed how fracture mechanics simulations can be conducted automatically for a large number of welded joints with heterogeneous geometries. Therefore, an integrated procedure is developed in which parametric simulation models are generated, fracture mechanically analysed and the results together with their metadata are saved in a selectable master file. Then, the fatigue lives are calculated from the numerical results via the Paris-Erdogan equation and compared with the experimentally determined data. It is shown that by adapting the Paris-Erdogan parameters, high accuracy can be achieved in predicting fatigue lives under sub-zero temperatures. Moreover, a method is described in which a low effort verification of the Paris-Erdogan parameters C and m, separately from each other, by comparing numerical and experimental fatigue lives in a logarithmic space.Publicationtype: Master Thesis62 111 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Holistic control of a multi-mode submerged wave energy converter(2022); Publicationtype: Doctoral Thesis50 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Ice-induced vibrations of vertical structures(2021-12-09); Vertical structures exposed to drifting level ice can exhibit significant ice-induced vibrations. However, their fundamental physical process is not sufficiently understood to date. Therefore, novel model tests in ice have been conducted utilizing local pressure mapping techniques to assess the influence of local failure processes on the occurrence of ice-induced vibrations. Analysis of the acquired data reveals a significant impact of the relative velocity between ice and structure on the local failure and contact development. Based on this finding, a prediction method and a scaling approach are developed.Publicationtype: Doctoral Thesis197 307 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , 63 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Ultimate strength of ship plating - A proof of capacity under combined in-plane loads(2016-11); The need for a proof of plate capacity under combined in-plane loads is addressed. An extensive series of numerical studies based on the finite element method is performed covering all load combinations and plating configurations relevant for the shipbuilding industry. These studies are used to investigate the mechanics of plating collapse and to evaluate existing proofs of plate capacity. In order to satisfy both qualitative and quantitative acceptance criteria, a new proof of plate capacity under combined in-plane loads is developed. Practical application of the proof in design is presented.Publicationtype: Doctoral Thesis510 1562 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Identification of material data of reinforced polyurethane foam used in membrane cargo containment systems for LNG tanks(2016); Publicationtype: Bachelor Thesis53